1. Field of the Invention
Generally disclosed herein are compositions that include a hydrophobic compound and a polyamino acid conjugate. The compositions described herein are useful for a variety of drug, biomolecule, and imaging agent delivery applications. Also disclosed are methods of using the compositions described herein to treat, diagnose, and/or image a subject.
2. Description of the Related Art
A variety of systems have been used for the delivery of drugs, biomolecules, and imaging agents. For example, such systems include capsules, liposomes, microparticles, nanoparticles, and polymers.
A variety of polyester-based biodegradable systems have been characterized and studied. Polylactic acid (PLA), polyglycolic acid and their copolymers polylactic-co-glycolic acid (PLGA) are some of the better characterized biomaterials with regard to design and performance for drug-delivery applications. See Uhrich, K. E., Cannizzaro, S. M., Langer, R. S., and Shakeshelf, K. M.; “Polymeric Systems for Controlled Drug Release,” Chem. Rev. 1999, 99, 3181-3198 and Panyam J, Labhasetwar V. “Biodegradable nanoparticles for drug and gene delivery to cells and tissue,” Adv. Drug. Deliv. Rev. 2003, 55, 329-47. Also, 2-hydroxypropyl methacrylate (HPMA) has been widely used to create a polymer for drug-delivery applications. Biodegradable systems based on polyorthoesters have also been investigated. See Heller, J.; Barr, J.; Ng, S. Y.; Abdellauoi, K. S, and Gurny, R. “Poly(ortho esters): synthesis, characterization, properties and uses.” Adv. Drug Del. Rev. 2002, 54, 1015-1039. Polyanhydride systems have also been investigated. Such polyanhydrides are typically biocompatible and may degrade in vivo into relatively non-toxic compounds that are eliminated from the body as metabolites. See Kumar, N.; Langer, R. S, and Domb, A. J. “Polyanhydrides: an overview,” Adv. Drug Del. Rev. 2002, 54, 889-91.
Amino acid-based polymers have also been considered as a potential source of new biomaterials. Poly-amino acids having good biocompatibility have been investigated to deliver low molecular-weight compounds. A relatively small number of polyglutamic acids and copolymers have been identified as candidate materials for drug delivery. See Bourke, S. L. and Kohn, J. “Polymers derived from the amino acid L-tyrosine: polycarbonates, polyarylates and copolymers with poly(ethylene glycol).” Adv. Drug Del. Rev., 2003, 55, 447-466.
Administered hydrophobic anticancer drugs, therapeutic proteins, and polypeptides often suffer from poor bio-availability. Such poor bio-availability may be due to incompatibility of bi-phasic solutions of hydrophobic drugs and aqueous solutions and/or rapid removal of these molecules from blood circulation by enzymatic degradation. One technique for increasing the efficacy of administered proteins and other small molecule agents entails conjugating the administered agent with a polymer, such as a polyethylene glycol (“PEG”) molecule, that can provide protection from enzymatic degradation in vivo. Such “PEGylation” often improves the circulation time and, hence, bio-availability of an administered agent.
PEG has shortcomings in certain respects, however. For example, because PEG is a linear polymer, the steric protection afforded by PEG is limited, as compared to branched polymers. Another shortcoming of PEG is that it is generally amenable to derivatization at its two terminals. This limits the number of other functional molecules (e.g. those helpful for protein or drug delivery to specific tissues) that can be conjugated to PEG.
Polyglutamic acid (PGA) is another polymer of choice for solubilizing hydrophobic anticancer drugs. Many anti-cancer drugs conjugated to PGA have been reported. See Chun Li. “Poly(L-glutamic acid)-anticancer drug conjugates.” Adv. Drug Del. Rev., 2002, 54, 695-713. However, none are currently FDA-approved.
Paclitaxel, extracted from the bark of the Pacific Yew tree, is a FDA-approved drug for the treatment of ovarian cancer and breast cancer. Wani et al. “Plant antitumor agents. VI. The isolation and structure of taxol, a novel antileukemic and antitumor agent from Taxus brevifolia,” J. Am. Chem. Soc. 1971, 93, 2325-7. However, like other anti-cancer drugs, pacilitaxel suffers from poor bio-availability due to its hydrophobicity and insolubility in aqueous solution. One way to solubilize pacilitaxel is to formulate it in a mixture of Cremophor-EL and dehydrated ethanol (1:1, v/v). Sparreboom et al. “Cremophor EL-mediated Alteration of Paclitaxel Distribution in Human Blood: Clinical Pharmacokinetic Implications,” Cancer Research, 1999, 59, 1454-1457. This formulation is currently commercialized as Taxol® (Bristol-Myers Squibb). Another method of solubilizing paclitaxel is by emulsification using high-shear homogenization. Constantinides et al. “Formulation Development and Antitumor Activity of a Filter-Sterilizable Emulsion of Paclitaxel,” Pharmaceutical Research 2000, 17, 175-182. Recently, polymer-paclitaxel conjugates have been advanced in several clinical trials. Ruth Duncan, “The Dawning era of polymer therapeutics,” Nature Reviews Drug Discovery 2003, 2, 347-360. More recently, paclitaxel has been formulated into nano-particles with human albumin protein and has been used in clinical studies. Damascelli et al., “Intraarterial chemotherapy with polyoxyethylated castor oil free paclitaxel, incorporated in albumin nanoparticles (ABI-007): Phase II study of patients with squamous cell carcinoma of the head and neck and anal canal: preliminary evidence of clinical activity.” Cancer, 2001, 92, 2592-602, and Ibrahim et al. “Phase I and pharmacokinetic study of ABI-007, a Cremophor-free, protein-stabilized, nanoparticle formulation of paclitaxel,” Clin. Cancer Res. 2002, 8, 1038-44. This formulation is currently commercialized as Abraxane® (American Pharmaceutical Partners, Inc.).
Magnetic resonance imaging (MRI) is an important tool in diagnosis and staging of disease because it is non-invasive and non-irradiating. See Bulte et al. “Magnetic resonance microscopy and histology of the CNS,” Trends in Biotechnology, 2002, 20, S24-S28. Although images of tissues can be obtained, MRI with contrast agents significantly improves its resolution. However, paramagnetic metal ions suitable for MRI contrast agents are often toxic. One of the methods to reduce toxicity is to chelate these metal ions with polydentate molecules such as diethylenetriamine pentaacetate molecules (DTPA). Gd-DTPA was approved by FDA in 1988 for clinical uses, and it is currently commercialized as Magnevist®. Other Gd-chelates were approved by FDA and commercialized, and many others are under development. See Caravan et al. “Gadolinium(III) Chelates as MRI Contrast Agents: Structure, Dynamics, and Applications,” Chem. Rev. 1999, 99, 2293-2352.
However, Gd-DTPA is not ideal for targeting tumor tissues because it lacks specificity. When Gd-DTPA is administered via IV injection, it spontaneously and rapidly diffuses into extravascular space of the tissues. Thus, large amounts of contrast agents are usually required to produce reasonable contrast images. In addition, it is quickly eliminated via kidney filtration. To avoid the diffusion and the filtration, macromolecular MRI contrast agents have been developed. See Caravan et al. “Gadolinium(III) Chelates as MRI Contrast Agents: Structure, Dynamics, and Applications,” Chem. Rev. 1999, 99, 2293-2352. These macromolecular-MRI contrast agents include protein-MRI chelates, polysaccharide-MRI chelates, and polymer-MRI chelates. See Lauffer et al. “Preparation and Water Relaxation Properties of Proteins Labeled with Paramagnetic Metal Chelates,” Magn. Reson. Imaging 1985, 3, 11-16; Sirlin et al. “Gadolinium-DTPA-Dextran: A Macromolecular MR Blood Pool Contrast Agent,” Acad. Radiol. 2004, 11, 1361-1369; Lu et al. “Poly(L-glutamic acid) Gd(III)-DOTA Conjugate with a Degradable Spacer for Magnetic Resonance Imaging,” Bioconjugate Chem. 2003, 14, 715-719; and Wen et al. “Synthesis and Characterization of Poly(L-glutamic acid) Gadolinium Chelate: A New Biodegradable MRI Contrast Agent,” Bioconjugate Chem. 2004, 15, 1408-1415.
Recently, tissue-specific MRI contrast agents have been developed. See Weinmann et al. “Tissue-specific MR contrast agents.” Eur. J. Radiol. 2003, 46, 33-44. However, tumor-specific MRI contrast agents have not been reported in clinical applications. Nano-size particles have been reported to target tumor-tissues via an enhanced permeation and retention (EPR) effect. See Brannon-Peppas et al. “Nanoparticle and targeted systems for cancer therapy.” ADDR, 2004, 56, 1649-1659).